Traditionally, overmolded electronic assemblies have utilized heat sink plates, having multiple integrated heat sink pedestals, as a primary thermal path for removing heat from flip-chip components mounted to a substrate of the electronic assembly. Usually, the heat sink plate has been made of a die cast aluminum and a thermal interface material has been placed between a flip-chip and its associated heat sink pedestal. Irrespective of whether an electronic assembly has been of a single plate or dual plate design, the heat sinks pedestals have been integrated into the plate. Unfortunately, utilizing a single plate with multiple integrated heat sink pedestals has required precise positioning and height tolerances for the pedestals. Typically, these precise height tolerances have required machining the pedestals formed on the single plate, usually as a secondary process. If the pedestals are not machined, the interface gap between the pedestal face and an associated flip-chip may be greater than desired, which, in turn, leads to poor heat transfer between the flip-chip and the pedestal.
During the overmolding process for an electronic assembly, it is common to use a Bellville-type washer to prevent plate bending, substrate cracking and damage to flip-chips and/or solder joints, due to relatively high mold clamp pressures. Even if the plate is machined, the Bellville-type washer is typically required, due to the tolerance stack-up between flip-chip-to-flip-chip and/or plate-to-plate and/or flip-chip-to-plate. During the overmold process, it is frequently difficult to adequately support the substrate to prevent damage to the substrate, due to the fill and pack pressures that typically exist in the overmold process. The lack of sufficient substrate support, due to the various electronic components, is known to lead to substrate warpage and/or cracking.
During the overmold process, when the overmold material is injected into the mold, pressures are typically unequal causing the substrate to flex. When the overmold material cures, the substrate may be set in a warped state, which can cause undesirable stresses on solder joints, connector pins, board traces, etc., which may cause the overmolded electronic assembly to experience a premature failure in the field. Further, in such electronic assemblies, the secondary heat path for removing heat from the flip-chip is not as good as it could be, as the heat flows from the substrate through the overmold material and then to ambient air.
What is needed is an overmolded electronic assembly that is economical to produce, less prone to tolerance stack-up and that provides better substrate support during the overmold process.